Identification, friend or foe (IFF) is an identification system designed for command and control. It uses a transponder that listens for an interrogation signal and then sends a response that identifies the broadcaster. … The broadest characterization is that of friend, enemy, neutral, or unknown.

How does an IFF work?

The principle of operation is really quite simple: an IFF interrogator sends out a coded radio signal to the aircraft. A special device on the aircraft, an IFF transponder, picks up the signal and sends a response to identify itself as friendly.

What are the different modes of IFF?

IFF is used by both military and civilian aircraft. Modes 1, 2, 4 and 5 are for military use only. Modes 1, 2 and 3/A are collectively known as Selective Identification Feature (SIF) modes. Civilian aircraft use modes 3/A, C and S.